1. Field of the Invention
The present invention relates to a lens control device equipped with a zooming lens mechanism, a method of controlling the lens control device, and a storage medium, and more particularly to a lens control device having a lens position control function for focusing, a method of controlling the lens control device, and a non-transitory computer-readable storage medium.
2. Description of the Related Art
Conventionally, as one of variable power systems used in a digital camera, a video camera, and so forth, there has been proposed e.g. a lens system LS which forms a zooming lens mechanism configured as shown in a part surrounded by a broken line in FIG. 1. This lens system LS is constructed by arranging, with respect to an image pickup device 4, a variable power lens 1 for performing magnification (including reduction) of an object image, a focus lens 2 having both of a focus adjustment function and a so-called compensator function for correcting deviation of a focal plane due to the magnification, and a diaphragm 3, in the mentioned order from an object side.
In the lens system LS configured as shown in the part of FIG. 1, the focus lens 2 has both of the compensator function and the focus adjustment function. Therefore, in this lens system LS, even when focal lengths are equal, the positional relationship between the variable power lens 1 and the focus lens 2 for focusing an object image on the imaging surface of the image pickup device 4 can vary depending on an object distance. Further, in the lens system LS, even if object distances are equal, when the focal length is changed by a zooming operation (a magnification operation), the position of the focus lens 2 for focusing on the imaging surface becomes different.
Further, in the lens system LS configured as shown in the part of FIG. 1, the variable power lens 1 is driven, as shown in FIG. 5, for a zooming operation, and at the same time, the movement of the position of the focus lens 2 is controlled so as to focus an object image on the imaging surface. In FIG. 5, the horizontal axis represents the variable power lens position (corresponding to focal length) and the vertical axis represents the focus lens position (corresponding to object distance), and the position of the focus lens 2 (focus lens position)is continuously plotted on an object distance-by-object distance basis, whereby the positional relationship between the variable power lens 1 and the focus lens 2 in the in-focus state is illustrated.
In the above-described lens control device, during the zooming operation, a trajectory of the focus lens position, which corresponds to the present object distance, is selected from those shown in FIG. 5, and the focus lens 2 is driven according to the trajectory, whereby a zooming operation with no blur is carried out.
In general, in the image pickup apparatus using the above-described lens system LS, to cause the lens system LS to perform the zooming operation while maintaining the in-focus state of an object image, it is a general practice to store information on the trajectories (hereinafter referred to as the “cam trajectories”) as shown in FIG. 5 in advance in some form or other in a lens control microcomputer, and perform zooming by reading out trajectory information corresponding to the present position of the variable power lens 1 and moving the focus lens 2 based on the trajectory information.
Further, in the conventional image pickup apparatus, there has been proposed a method of storing in advance respective positions of the focus lens 2 where focus can be achieved at a plurality of positions of the variable power lens 1 spaced from each other, according to each object distance, and calculating a focus lens position where focus can be achieved at the current variable power lens position during the zooming operation, based on the relationship between the current position of the variable power lens 1 and a stored position of the variable power lens 1 adjacent to the current variable power lens position (see Japanese Patent Registration No. 02790812 and Japanese Patent Laid-Open Publication No. H09-005604).
However, in the above-described conventional method of calculating a focus lens position where focus can be achieved at the current variable power lens position using the stored variable power lens positions, each stored cam trajectory is limited to a range wherein the focus lens position can be set according to the zooming operation of the variable power lens 1.
More specifically, the conventionally proposed method is for calculating a focus lens position in a range from a wide-angle end to a telephoto end of the variable power lens position, and therefore cannot cope with e.g. a hatched area in FIG. 6, beyond the telephoto end.
Actually, however, the variable power lens position is sometimes displaced toward a super wide-angle position beyond the wide-angle end or toward a super telephoto position beyond the telephoto end, i.e. into the hatched area appearing in FIG. 6, due to a position control error of the variable power lens position, such as a stopping error of the variable power lens 1, an attitude error of the lens system, etc.
In this case, when the position control of the focus lens 2 is performed by the above-described conventional method, since there is no cam trajectory at the super telephoto position, a focus lens position associated with the stored telephoto end has to be selected. That is, if the degree of the stop position error of the variable power lens 1 is large, it is impossible to achieve focus when zoomed to the vicinity of the telephoto end. The same problem also occurs with the wide-angle side.